Unloader and overload protector for rotary compressors



M r 9, 1954 v. J. GRUMBLATT UNLOADER AND OVERLOAD PROTECTOR FOR ROTARYCOMPRESSORS Filed Aug. 27, 1949 Inventor- F ww w J. m m m H V9 .D

Patented Mar. 9, 1954 UNLOADER AND OVERLOAD PROTECTGR FOR ROTARYCOMPRESSORS Victor J. Grumblatt, East Cleveland, Ohio, assignor toGeneral Electric Company, a corporation of New York Application August27, 1949, Serial No. 112,787

12 Claims. 1

My invention relates to compressors and more particularly to rotarycompressors.

In the operation of compressors it is frequently desirable to makeprovision for unloading, particularly during the starting operation inorder to reduce the load on the motor used for driving the compressor.Such unloading may be accomplished, for example, by providing freecommunication between the inlet and discharge ports of the compressor.Similarly, it may be desirable to provide such communication during thesubsequent operation of the compressor in the event an overload shouldoccur for any reason. By my invention I have provided a simplearrangement which facilitates unloading of a compressor and alsoprotects'the motor against undesirable overloads.

It is an object of my invention to provide an improved unloadingarrangement for a rotary compressor.

It is another object of my invention to provide an improved overloadprotector for a rotary compressor.

Further objects and advantages of my invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming part of this specification.

In carrying out the objects of my invention, I provide an arrangementfor automatically moving the blade of the rotary compressor out ofengagement with the rotor during all or a portion of each revolution ofthe rotor in response to the load on the driving motor. Alternatively,only one part of a multi-part blade may be moved to reduce the load.More specifically, the position of the blade or the movable part of theblade is controlled by a solenoid whose energization is dependent on theload on the motor.

For a better understanding of my invention reference may be had to theaccompanying drawing in which Fig. 1 is a schematic diagram illustratingan embodiment of my invention; Fig. 2 is a view of a portion of theapparatus of Fig. 1 under different conditions; Fig. 3 is a schematicdiagram illustrating a modified form of my invention; Fig. 4 showsanother modified form of my invention; Fig. 5 is a view similar to Fig.4 illustrating the position of the parts under different conditions;Fig. 6 shows another modified form of my invention; and Fig. 7 is a viewsimilar to Fig. 6 illustrating the position of the parts under'differentconditions.

Referring to -Fig. 1, there is shown a rotary compre'ssoriwhich isdriven by an electric motor 2. The electric motor includes a startingwinding 3 and a running winding 4. Power is supplied to these windingsfrom any suitable power source through lines 5, 6.

The rotary compressor includes a housing 1 within which a rotor t iseccentrically mounted and is driven by the motor 2. The rotor 8 rotateswithin a chamber S provided within the housing I of the compressor. Thecompressor includes an inlet port ill and a discharge port ll both ofwhich are in communication with the chamber d. Fluid pumped by thecompressor is supplied to the inlet port [0 through a conduit l2 and isdischarged from the discharge port ll through a conduit [3.

In order to block communication between the inlet and discharge ports inand H during the normal operation of the compressor 'a conventionalblade I is slidably received within the housing '5 and engages theperiphery l5 of the rotor. The blade It is biased into engagement withthe periphery it of the rotor by a compression spring It, one end ofwhich bears against a stationary stop I? and the other end of whichbears against a shoulder 18 of the blade I l.

The arrangement thus far described involves a conventional rotarycompressor structure in which, as the rotor 8 is rotated in thedirection indicated by the arrow, fluid is taken in through the inletport it, is moved through the chamber 9, and is discharged through thedischarge port ll. However, when compressors are employed, for example,in refrigerating systems there may be a substantial difference inpressure between the low, or inlet side, and the high or discharge side,particularly during the starting operation, and this imposes a heavyload on the driving motor 2. In order to reduce this load until themotor has had an opportunity to come up to speed and is able to assumethe load, I have provided an arrangement for automatically withdrawingthe blade Hi from engagement with the periphery l5 of the rotor 8. Itcan be seen that moving the blade out of engagement with the rotorpermits free communication between the inlet port and the discharge portthrough the chamber 9 and hence substantially eliminate the pumping loadon the motor 2. To accomplish this purpose a solenoid i9 is providedabout a portion 29 of the blade i l. The solenoid I9 is connected in acircuit 21 in series with the starting winding 3. In a conventionalarrangement a switch is arranged in series with the starting winding,the switch being arranged to interrupt the starting winding circuitafter the motor has come up to speed. The operation of the switch may bebased on the speed of the motor, the current through the startingwinding, etc. Such a switch has been shown at 22 in this figure but itwill become apparent that, insofar as the operation of the solenoid I9is concerned, the switch 22 could be omitted and a closed circuitutilized.

During normal operation the current through the winding 3 and thesolenoid l9, even should the switch 22 be omitted, is sufliciently lowthat any biasing force exerted by the solenoid I9 is exceeded by theopposing bias of the spring I6, and the blade I4 is maintained inengagement with the periphery I5 of the rotor 8. However, during thestarting operation a much heavier current flows through the windings ofthe motor 2 and hence through the solenoid I9, which is arranged inseries with the starting winding 3 of the motor. Under thesecircumstances the force exerted by the solenoid I9 on the armatureportion of the blade I4 exceeds the force exerted by the spring and theblade is moved out of engagement with the rotor to the position shown inFig. 2, wherein the upper end of the blade I4 engages the stop II andthe lower end of the blade I4 is moved out of the chamber 9 and ispositioned Within the housing I. This allows communication through thechamber 9 between the ports I0 and I I and hence efiects an unloading ofthe compressor. As the motor comes up to speed the current through thewindings decreases and hence the current through the solenoid I9correspondingly decreases, and the blade I4 is again moved intoengagement with the rotor 8 by the spring I5, instituting normaloperation of the compressor. The motor, having come up to speed, isreadily able to assume the necessary pumping load.

The operation of the device in the case of an overload occurring duringthe regular operation of the compressor is the same as that involved inthe unloading operation just described. Should an overload occur for anyreason the resultant increase in current through the motor windings isreflected in the energization of the solenoid I9 and the movement of theblade I 4 out of engagement with the rotor. This substantially reducesthe pumping load on the motor and minimizes the danger of overloaddamage to the motor.

The modified form shown in Fig. 3 differs from that described above onlyin that the solenoid I9 is arranged in series with the running winding 4in lieu of the starting winding 3. The same numerals have been used todesignate corresponding parts. During the starting operation there is aheavier current through the running winding 4 than durin the normaloperation of the compressor and hence a larger energizing currentthrough the solenoid I 9. The resultant energization of the solenoid I9is effective through the armature 20 to move the blade I4 out ofengagement with th periphery I5 of the rotor, un-

loading the compressor in the same manner as previously described.Similarly, should an overload occur, the increased current through thewinding 4 is also reflected in increased current through the solenoid I9and the blade I4 is moved out of engagement with the rotor 8 by thesolenoid I9.

In Figs. 4 and 5 there is illustrated a modified form of my invention inwhich the blade is only partially withdrawn from the chamber 9 so as toremain out of engagement with the rotor during only a portion of eachrevolution. The same numerals have been used to designate correspondingparts in Figs. 1, 2, and 3 and in Figs. 4 and 5. Referring to Figs. 4and 5 there is shown the rotary compressor I including the housing 1providing the chamber 9 within which the eccentrically-mounted rotor 8rotates. Inlet and discharge ports I0 and II, respectively, areillustrated. A blade 23 extends through the housing I and is biasedtoward engagement with the periphery I5 of the rotor 8 by a spring 24.During normal operation of the compressor the blade is compressed intoengagement with the periphery I5 of the rotor during the entirerevolution of the rotor. In order to provide for shifting the bladeunder certain conditions, for example, to unload the compressor, asolenoid I9 is utilized, this solenoid being connected in series withthe starting winding 3 or running winding 4 as lllustrated in Figs. 1and 3. The solenoid I9 controls the position of an armature 25 which iarranged to engage a portion 26 of the blade 23. In the position shownin Fig. 4, which corresponds to the normal operating condition of thecompressor, the armature 25 is biased downwardly against a stop 21 by aspring 28 and the engaging portion of the armature is spaced slightlybelow the portion 26 of the blade 23 so as not to interfere with themovement of the blade under the influence of the rotor 8 and the spring24. During starting of the motor or during overload conditions thecurrent through the starting or running winding and hence through thesolenoid I9 increases substantially. Under these conditions the solenoidI9 moves the armature 25 to the position shown in Fig. 5 wherein aportion 29 of the armature engages the stop I! and the armature engagesthe portion 28 of the blade 23 and moves the blade upwardly to theposition shown in Fig. 5. The stop I! and the spacing between the stopand the portion 29 of the armature 25 during normal operating conditionsare arranged so that the maximum travel of the armature moves the tip orend 30 of the blade 23 only partially out of the chamber 9 of thecompressor. Thus, in the position of the rotor 8 shown in Fig. 5 theblade 23 is held out of engagement with the rotor. However, it can beseen that during a portion of each revolution of the rotor the peripheryI5 of the rotor will engage the tip 30 of the blade 23 and during thisportion of each revolution refrigerant is pumped by the compressor inthe normal manner. When the motor has come up to speed during thestarting operation or when an overload occurring for any other reasonhas passed, the energization of the solenoid I9 is reduced and thearmature 25 returns to the position shown in Fig. 4, allowing normalmovement of the blade 23 and normal operation of the compressor.

In Figs. 6 and 7 there is shown another modified form of my inventionwhich employs a two-part blade in which one part of the blade remains inengagement with the rotor at all times. The same numerals have been usedto designate corresponding parts in Figs. 6 and 7 and in the precedingfigures. Referring to Fig. 6 wherein the position of the parts isillustrated for normal operation of the compressor there is shown ablade 3I extending through the housing I between the inlet port I9 andthe discharge port II. The blade 3I is made of two relatively movableparts 32 and 33. The part 32 is pressed into engagement with theperiphery of the rotor 8 by a spring 34 in a conventional manner. Oneend of the spring 34 engages a stop 35 and the other end presses againstan end 35 of the blade part 32. A recess 31 is provided in one side ofthe part 32 of the blade and the part 32 of the blade is arranged toslide within this recess. The position of the blade part 33 iscontrolled by the solenoid I9 which is arranged in series with thestarting winding or the running winding of the motor as illustrated inFigs. 1 and 3. The blade part 33 is normally pressed downwardly againsta shoul- 5 der 38 on the blade part 32 by a spring 39 which engages thestop I! and an armature portion 40 of the blade part 33.

A transverse passage 4| is provided in the blade part 32 for permittingcommunication between the ports l and l I under certain conditions ofoperation. Under normal conditions, as illustrated in Fig. 6, the slightenergization of the solenoid i9 is overbalanced by the force exerted bythe spring 39 and the blade part 33 is held in engagement with theshoulder 38, blocking the passage 4|. Under these conditions the blade3i acts in the same manner as a. solid one-piece blade of a conventionalcompressor and fluid is pumped by the compressor in the conventionalmanner. Under starting conditions or under other conditionswherein anexcessive load is imposed on the motor the increase current through thesolenoid l9 moves the armature 4i! and the blade part 33 upwardly beyondthe end 42 of the passage il, as illustrated in Fig. '7. It can be seenthat, in this position of the blade part 33, the passage 4| provides forcommunication through the blade between the inlet port ill and thedischarge port H, unloading the compressor. When the rotor 8 has turnedsufficiently to move the blade upwardly to a point where the shoulder 38and the lower edge 43 of the passage 4| are just within the housing 1communication through the passage M is blocked by the housing itself andhence the compressor operates to pump fluid in the normal manner duringthis portion of each revolution. In this respect the modified form shownin Figs. 6 and 7 operates in a manner similar to the form shown in Figs.4 and wherein, even under unloading conditions, the compressor iseffective to pump fluid during a portion of each revolution.

While I have shown and described specific embodiments of my invention, Ido not desire my invention to be limited to the particular constructionsshown and described, and I intend, by the appended claims, to cover allmodifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, a rotary compressor and an electric motor for drivingsaid compressor, said compressor including a housing having a chambertherein and a rotor eccentricall'y-mounted within said chamber, saidhousing including spaced inlet and discharge ports, a blade extendingthrough said housing between said ports, said blade being normallybiased into engagement with said rotor, and electromagnetic meansconnected in series with said motor for positively moving at least aportion of said blade in a direction away from said rotor to providecommunication between said inlet and said discharge ports for unloadingsaid compressor during at least a portion of each revolution of saidrotor in response to a predetermined maximum current supplied to saidmotor.

2. In combination, a rotary compressor and an electric motor for drivingsaid compressor, said compressor including a housing having a chambertherein and a rotor eccentrically-mounted within said chamber, saidhousing including spaced inlet and discharge ports, a blade extendingthrough said housing between said ports, saidblade being normally biasedinto engagement with said rotor, and electromagnetic means connected inseries with said motor for positively moving said blade away from saidrotor to provide communication between said inlet and said dischargeports for unloading asid compressor in response to a predeterminedmaximum current supplied to said motor.

3. In combination, a rotary compressor and an electric motor for drivingsaid compressor, said compressor including a housing having a chambertherein and a rotor eccentrically-mounted within said chamber, saidhousing including spaced inlet and discharge ports, a blade extendingthrough said housing between said ports, said blade being normallybiased into engagement with said rotor, a solenoid having an armaturearranged for movement in the direction of movement of said blade forpositively moving at least a portion of said blade in a direction awayfrom said rotor to provide communication between said inlet and saiddischarge ports for unloading said compressor during at least a portionof each revolution of said rotor, and means dependent on the load onsaid motor for energizing said solenoid to move at least said portion ofsaid blade out of engagement with said rotor.

4. In combination, a rotary compressor and an electric motor for drivingsaid compressor, said compressor including a housing having a chambertherein and a rotor eocentrically-mounted within said chamber, saidhousing including spaced inlet and discharge ports, a blade extendingthrough said housing between said ports, said blade being normallybiased into engagement with said rotor, a solenoid having an armaturearranged for movement in the direction of movement of said blade forpositively moving said blade away from said rotor to providecommunication between said inlet and said discharge ports for unloadingsaid compressor during at least a portion of each revolution of saidrotor, and means dependent on the load on said motor for energizing saidsolenoid to move said blade out of engagement with said rotor.

5. In combination, a rotary compressor and an electric motor for drivingsaid compressor, said compressor including a housing having a chambertherein and. a. rotor eccentrically-mounted within said chamber, saidhousing including spaced inlet and discharge ports, a blade extendingthrough said housing between said ports, said blade being normallybiased into engagement with said rotor, a solenoid having an armaturearranged for movement in the direction of movement of said blade forpositively moving said blade away from said rotor to providecommunication between said inlet and said discharge ports for unloadingsaid. compressor, and means dependent on the load on said motor forenergizing said solenoid to move said blade out of engagement with saidrotor.

6. In combination, a rotary compressor and an electric motor for drivingsaid compressor, said compressor including a housing having a chambertherein and a rotor eccentrically-mounted within said chamber, saidhousing including spaced. inlet and discharge ports, a blade extendingthrough said housing. between said ports, said blade including tworelatively movable parts, one of said parts of said blade being biasedinto engagement with said rotor, said one of said parts of said bladehaving a passage therein for providing communication between said inletport and said discharge port, the other of said parts of said bladebeing normally biased to one position to block communication throughsaid passage, a solenoid for shifting said other of said parts of saidblade to a second position out of blocking relationship with saidpassage to provide communication between said inlet port and saiddischargeport for unloading said compressor during at least a portion ofeach revolution of said rotor, and means dependent on the load on saidmotor for energizing said solenoid to move said other of said parts ofsaid blade to its second position.

7. In combination, a rotary compressor and an electric motor for drivingsaid compressor, said compressor including a housing having a chambertherein and a rotor eccentrically-mounted within said chamber, saidhousing including spaced inlet and discharge ports, a blade extendingthrough said housing between said ports, said blade being normallybiased into engagement with said rotor, and a solenoid for positivelymoving at least a portion of said blade in a direction away from saidrotor to provide communication between said inlet and discharge portsfor unloading said compressor during at least a portion of eachrevolution of said rotor, said solenoid being connected in series withsaid motor whereby energization of said solenoid is dependent on currentflow to said motor.

8. In combination, a rotary compressor and an electric motor for drivingsaid compressor, said motor including a starting winding and a runningwinding, said compressor including a housing having a chamber thereinand a rotor eccentrically-mounted within said chamber, said housingincluding spaced inlet and discharge ports, a blade extending throughsaid housing between said ports, said blade being normally biased intoengagement with said rotor, and a solenoid for positively moving atleast a portion of said blade in a direction away from said rotor toprovide communication between said inlet and discharge ports forunloading said compressor during at least a portion of each revolutionof said rotor, said solenoid being connected in series with one of saidwindings of said motor whereby energization of said solenoid isdependent on current flow through said one of said windings.

9. In combination, a rotary compressor and an electric motor for drivingsaid compressor, said compressor including a housing having a chambertherein and a rotor eccentrically-mounted within said chamber, saidhousing including spaced inlet and discharge ports, a blade extendingthrough said housing between said ports, a spring for biasing said bladeinto engagement with said rotor, a solenoid having an armature arrangedfor movement in the direction of movement of said blade for positivelymoving said blade away from said rotor in opposition to said spring toprovide communication between said inlet and discharge ports forunloading said compressor, and means dependent on a load condition ofsaid motor for energizing said solenoid to move said blade out ofengagement with said rotor.

10. In combination, a rotary compressor and an electric motor fordriving said compressor, said compressor including a housing having achamber therein and a rotor eccentrically-mounted within said chamber,said housing including spaced inlet and discharge ports, a bladeextending through said housing between said ports, a spring for biasingone end of said blade into said chamber and into engagement with saidrotor, a solenoid having an armature arranged for movement in thedirection of movement of said blade for positively moving said bladeaway from said rotor and out of said chamber to provide communicationbetween said inlet and discharge ports for unloading said compressor,and means dependent on a load condition of said motor for energizingsaid solenoid to move said blade.

11. In combination, a rotary compressor and an electric motor fordriving said compressor, said compressor including a housing having achamber therein and a rotor eccentrically-mounted within said chamber,said housing including spaced inlet and discharge ports, a bladeextending through said housing between said ports, a spring for biasingone end of said blade into said chamber and into engagement with saidrotor, a solenoid having an armature arranged for movement in thedirection of movement of said blade for positively moving said bladeaway from said rotor to provide communication between said inlet portand said discharge port for unloading said compressor, means dependenton a load condition of said motor for energizing said solenoid, andmeans for limiting the movement of said blade away from said rotor sothat said one end of said blade rejects into said chamber when saidsolenoid is energized whereby said rotor engages said blade during aportion of each revolution to effect normal pumping action during saidportion of each revolution.

12. In combination, a rotary compressor and an electric motor fordriving said compressor, said compressor including a housing having achamber therein and a rotor eccentrically-mounted within said chamber,said housing including spaced inlet and discharge ports, a bladeextending through said housing between said ports, said blade includingtwo relatively movable parts, a spring for biasing one end of one ofsaid parts of said blade into said chamber and into engagement with saidrotor, said one of said parts having a passage therein for providingcommunication between said inlet port and said discharge port, a springfor biasing the other of said parts of said blade normaly to oneposition to block communication through said passage, a solenoid forshifting said other of said parts of said blade to a second position outof blocking relationship with said passage to provide communicationbetween said inlet port and said discharge port for unloading saidcompressor, and means dependent on a load condition of said motor forenergizing said solenoid to move said other of said parts of said bladeto its second position, said passage being spaced from said one end ofsaid one part of said blade a distance such that said passage portion ofsaid one part of said blade is moved out of said chamber into saidhousing during a portion of each revolution of said rotor wherebycommunication between said inlet port and said discharge port throughsaid passage is blocked by said housing during said portion of eachrevolution of said rotor regardless of the position of said other partof said blade.

VICTOR J. GRUMBLATT.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 974,913 Von Pittler Nov. 8, 1910 1,912,463 Ploeger June 6,1933 2,007,388 Tarleton July 9, 1935 2,020,987 Ayres Nov. 12, 19352,069,767 McCormack Feb. 9, 1937 2,458,018 Murphy Jan. 4, 1949 2,488,942Schweller Nov. 22, 1949 FOREIGN PATENTS Number Country Date 209,715Switzerland Aug. 1, 1950

